Inflammatory processes, often amenable to address by non-steroidal anti-inflammatories such as ibuprofen, naproxen, indomethacin and diclofenac, are inherent in the pathologies of multiple sclerosis, Alzheimer's disease, depression, amyotrophic lateral sclerosis, dementia, Parkinson's disease, and other neurodegenerative states. Several of these diseases are also independently characterized by perturbation of cholinergic balance and hence therapies combining cholinesterase inhibitors and inflammation mediators are believe to represent a dual benefit.
The chronic use of indomethacin and other NSAIDs either in prophylaxis or in therapy risks adverse gastrointestinal effects, renal toxicity, allergic responses, and occasionally severe ulcerations. A highly lipophilic ester “pro-drug” of indomethacin [DP-155] has been claimed to deliver enhanced brain levels while markedly decreasing both renal and gastrointestinal toxicities (E. Dvir, A. Elmann, D. Simmons, I. Shapiro, R. Duvdevani, A. Dahan, A. Hoffman, and J. E. Friedman, CNS Drug Rev. 2007, 13: 260-277). The pro-drug conjugate was efficacious in reducing levels of amyloid ss (Ass)42 in a transgenic Alzheimer's disease mouse (Tg2576). In DP-155, a methylene chain spacer separated the indomethacin ester from the ester at the lipid carrier terminus. For this purpose, a five carbon spacer was shown to be 20-fold better in transmembrane absorption than a short two-carbon spacer (A. Dahan, R. Duvdevani, E. Dvir, A. Elmann, and A. Hoffman, J. Control Release 2007, 119: 86-93).
Orally-administered NSAID-esters of basic aminoalcohols are reported to be competitive reversible inhibitors of AChE and to reduce intestinal gastric ulceration often associated with the non-conjugated NSAID carboxylic acids or their salts (P. K. Halen, K. K. Chagti, R. Giridhar, and M. R. Yadav, Chem. Bio. Drug Des. 2007: 70: 450-455). The cholinergic anti-inflammatory pathway is a high value therapeutic target readily justifying the combination of anti-cholinergic and anti-inflammatory activity into a single molecule. Wang has noted that binding at the acetylcholine receptor is a down-regulatory mechanism for inflammation (H. Wang et al., Nature 2003, 421: 384-388).
Amitai has shown that the combination of an anti-inflammatory (ibuprofen or diclofenac) and an inhibitor of acetylcholinesterase into the same molecule provided a therapeutic benefit in the treatment of inflammation resulting from chemical blistering agents (A. Amitai, R. Adani, E. Fishbein et al., J. Applied Tox., 2006, 26: 81-87). Although doubly functionalized with an NSAID and an anti-cholinergic, in this case the two moieties could not be independently liberated in vivo. Thus there remains a need for additional moieties that can be independently liberated in vivo.
This application relates to a unique lipophilic pro-drug of an NSAID such as indomethacin (or other NSAIDs) which is simultaneously a competitive reversible inhibitor of acetylcholinesterase and a controlled release carrier of the NSAID. These pharmaceuticals are unsymmetrical alkyl-aryl carbonates whose —O—CO—O— bond is readily cleaved both by chemical hydrolysis and esterolytic activity, thereby freeing an NSAID by a facilitated hydrolysis. Since the NSAID is directly attached to the platform by a hydrolyzable ester function, there are two modes by which the NSAID is made available.
Accordingly, one embodiment of the invention relates to a compound of Formula 1 wherein
wherein
n is 0 or 1;
X is Si, C, or N+;
wherein when X is C or N+, each R is alike or different and is hydrogen or (C1-C6) alkyl;
when X is Si, each R is methyl; and
NSAID is a non-steroidal anti-inflammatory agent.
The high level of esterase activity (arising from native acetylcholinesterases, carboxyesterases, and related esterases) found in human skin, epidermal membranes, and plasma, makes ester-containing pro-drugs attractive targets as drug-delivery vehicles for topical or oral formulations (J. L. Prusakiewicz, C. Ackermann, and R. Voorman, Pharmaceutical Research 2006, 23: 1517-1524). Other studies have shown that a carbonate-linkage (—O—CO—O—) is always very similar in behavior to an ester-linkage as the hydrolysable function joining drug to carrier (J. Rautio et al., Nature Reviews Drug Discovery 2008, 7: 255-270). In a limited set of 17 analogs, Vaddi compared esters to carbonates as pro-drug linkers to naltrexone and found the carbonates to have a faster transdermal flux rate and to be slightly more resistant to hydrolysis in the skin (enzymatic and hydrolytic) itself than was the case with the esters. More esters were cleaved in the skin leaving lower quantities available for penetration and transport in the plasma. The differences in absorption rate and hydrolysis rate between esters and carbonates were real but were not large (H. K. Vaddi, et al. Pharmaceutical Research, 2005, 22: 758-765). As far as purely chemical cleavage, most carbonates were less reactive to hydrolysis in acid or in base than were esters (J. Ostergaard and C. Larsen, Molecules, 2007, 12: 2396-2412).
The use of the construct p-(X-methyl)phenol (or an ester or carbamate of it) as a platform for the release of two molecular fragments in vivo—both of which in some cases possess biological activity—has been applied by accident and by deliberate design in several agricultural and pharmaceutical products. The principle displayed here is that electron delocalization from the phenolic oxygen provides an indirect cleavage pathway for an anionic species (viz., p-X—CH2—C6H4—O—R if converted by cleavage at R to p-X—CH2—C6H4—O− will liberate X−). The presumed electron pathway is shown below. The attack at R is usually a hydrolysis at a carbonyl.

In the nitric oxide donating aspirin conjugate known as NO-ASA, R in the structure shown above is aspirin (acetylsalicylic acid) linked at its carboxylic moiety and X is the NO-precursor —O—NO2. Promising results have been reported against colon, pancreatic, and breast cancers as well as in protection of gastric mucosal irritation and enhancement of in situ antioxidant events. (J. L. Williams, P. Ji, N. Ouyang, X. Liu, B. Rigas, Carcinogenesis 2008, 29, 390-397 and S. Kwiecien, M. W. Pawlik, T. Brzozowski, et al, J. Physiol Pharmacol. 2008 Suppl 2:103-15). The in vivo release of thalidomide and nitric oxide from a conjugate drug in which R in the structure above is the carbamate of thalidomide and X is the NO-precursor —O—NO2 arrested the growth of malignant liver cells (T. Wang, Y. H. Zhang, H. Ji, et al., Chinese Chemical Letters, 2008, 19: 26-28). Immonium chlorides derived from DMF and 4-(chloromethyl)phenyl chloroformate (X in above formula=Cl, R═CH═N+Me2) hydrolyzed to useful bactericides presumably by the indicated mechanism but not recognized as such by the authors (V. A. Pattison and R. L. K. Carr, U.S. Pat. No. 3,983,178). In a family of pro-pesticides which hydrolyzed to potent acaricides by the general structure shown above, R=—P(═O)OR/SR′ and X=—SCH3. (R. Sehring, W. Buck, R. Prokic-Immel, S. Lust, Ger. Offen. DE 3223949, 1983 and W. Buck, G. Geisthardt, R. Prokic-Immel, R. Sehring, Dokl. Soobshch-Mezhdunar. Kongr. Zashch. Rast., 8th 1975, 3: 50-57).
As a general class, these substances—with n=0, 1 and X═C, Si, and N+— can be described as:

Variation in the alkyl function provides the recognition moiety for the target enzyme with choline-like mimics such as —CH2CH2T(Me)3 [wherein T=N+, Si, or C] providing the traditional molecular architecture required for site affinity at acetylcholinesterase. Even though the structural shift from a water-soluble trimethyl ammonium [+NMe3] to a trimethyl carbon [—C(CH3)3] or to a trimethyl silyl [—Si(CH3)3], means an increasing hydrophobicity, these moieties can nevertheless by recognized and bound to acetylcholinesterase. As Cohen phrased it in reference to the quat silyls and quat carbons, . . . “the enzyme stands nearby ready to bind and try to hydrolyze and remove compounds that even superficially resemble the natural agonist.” (S. G. Cohen, S. B. Chishti, J. L. Elkind, H. Reese, and J. B. Cohen, J. Med. Chem. 1985, 28: 1309-1313). Variation of n=1 to n=0 allows the incorporation or non-incorporation of a p-hydroxybenzyl alcohol linker moiety whose presence increases the lipophilicity of the final construct by 1.9 log units (cLogP, a computed quantity for hydropholic/hydrophilic molecular property). In addition to adding lipophilicity when desired, this linker (when present) provides two sites of controlled hydrolytic/enzymatic release of the NSAID at a carbonate and at an ester functionality.